1. Field of the Invention
This invention relates to bone joint prosthesis. More specifically, it concerns an elbow endoprosthesis providing good joint stability with allowance for normal flexion and extension motion at the elbow.
2. Description of the Prior Art
Use of bone joint prosthesis may be indicated for use for various derangements of the joint in which reasonable function has been lost and where there is significant stiffening and/or pain. Such conditions include osteoartheosis, which is usually secondary to trauma in the case of the elbow, rheumatoid disease and neuropathic arthropathy where there is, typically, instability.
Joint stability is a critical factor in the mobilization of weight-bearing joints as in the reconstruction of the hip and knee. It is also important in the non-weight-bearing elbow joint. On the other hand, in the elbow, unlike many other joints, no position of ankylosis is favorable to function; there may be a particular problem with regard to loss of upper limb function in the rheumatoid patient because of concomitant disease elsewhere in the limb. In short, the elbow presents special problems in prosthetic reconstruction. Hence, the following description is directed primary to elbow prosthesis, but the procedures and devices as described can find application in other bone joint reconstructions.
A variety of procedures and devices have been devised for elbow prosthetic reconstruction. Excision arthroplasty has been historically used and may involve partial or total resection of the elbow joint. Certain indications, for this operation are tuberculosis, recent comminuted fracture, old un-reduced fracture-dislocation, rheumatoid arthritis and osteoarthritis following injury. Although many patients have obtained worthwhile results, this has not been a universally successful procedure.
Early attempts at replacement arthroplasty involved the use of various materials to surface the reconstructed elbow joint: muscle and fascial flap, periosteal flaps, yellow wax and lanolin, magnesium and other metal sheets, deep fascia from the thigh and skin from the buttock. None of these have yet received popular acceptance and most are now probably of historical interest only.
In recent times there has been increasing interest in replacement arthroplasty of the elbow joint.
Partial, or hemi, replacement of the joint has been described: acrylic replacement of the distal humerus, vitallium replacement of the distal humerus, vitallium replacement of the olecranon and silastic replacement of the radial head.
Attempts have now been made to functionally replace the elbow as a whole by a `total elbow prosthesis`. The majority of these consist of a hinge device with three parts (humeral component, ulnar component and an axis pin): all require a significant removal of bone, soft tissue dissection and reaming of the humeral and ulnar shafts in order to seat the stems of the prosthesis, which are cemented in place. Examples of this type of prosthesis include metal stems with plastic and metal axis or metal stems and metal axis. There is a more recent prosthesis which consists of two metal stems with a high density polyethylene `clip-on` device for locking the two together, but with this there is a great deal of side-to-side instability. Another total elbow prosthesis consists of simple surfacing of the humerus with metal and the ulna with high density polyethylene. Also there is a one-piece silastic hinge with the stems inserting into the humerus and ulna; but here medial and lateral instability has to be controlled by constructing new collateral ligaments from fascia.
In so far as structural bone joint prosttheses are concerned, numerous patents have issued covering such devices of which the following is a representative listing: U.S. Pat. Nos. 2,784,416; 3,748,662; 3,798,679; 3,801,990; 3,840,905; 3,869,729 and 3,886,599.
The normal elbow is a simple and stable hinge joint permitting only flexion and extension; forearm rotation occurs at the radio-ulnar joints and the superior radio-ulnar joint is enclosed with the elbow joint in a common capsule. Severe restriction of movement or in stability of the elbow is difficult to treat. Excision arthroplasty has the distinct potential for significant instability, likewise the various joint lining procedures. Hemi-arthroplasties, as for the humerus or olecranon, do not deal with what is usually total joint surface involvement. The many hinge joints with an axis demand considerable removal of bone for insertion: many of these fail, with loosening of one or both stems of the prosthesis, and necessary removal of such a prosthesis results in serious instability of the elbow.
In spite of the numerous procedures and devices previously developed and used for elbow reconstruction, there exists a need for further improvement particularly as regards resulting joint stability, minimal removal of bone for insertion and allowance for normal flexion and extension motion.